Semiconductor integrated circuit for wireless communication

Abstract

A semiconductor integrated circuit with a PLL (Phase Locked Loop) built therein is used in a semiconductor integrated circuit for wireless communication. The PLL circuit generates an oscillation signal having a predetermined frequency, which is combined with a receive signal or a transmit signal for wireless communication. The PLL circuit includes a VCO capable of switching an oscillation frequency band, a variable divider, a loop filter and a phase comparator. An oscillation frequency of the VCO is controlled according to the difference in phase between a signal obtained by dividing the output of the VCO and a reference signal, and a discrimination circuit makes a decision as to a lead or delay of the phase of an output of the variable divider with respect to a reference signal having a predetermined frequency. An auto band selection circuit generates a signal for selecting a frequency band for the VCO.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] The present application claims priority from Japanese patent application No. 2004-210289 filed on Jul. 16, 2004, the content of which is hereby incorporated by reference into this application. BACKGROUND OF THE INVENTION [0002] The present invention relates to a technique effective if applied to a semiconductor integrated circuit with a PLL (Phase Locked Loop) built therein, and relates to, for example, a technique effective if used in a semiconductor integrated circuit for wireless communication, which incorporates therein a PLL circuit that generates an oscillation signal having a predetermined frequency, which is combined with a receive signal or a transmit signal for wireless communication. [0003] In a wireless communication system like a cellular phone, a high-frequency semiconductor integrated circuit (hereinafter called “high-frequency IC”) has been used which includes a PLL circuit including an oscillator that generates a local o...

AI Technical Summary

Benefits of technology

[0023] Advantageous effects obtained by typical ones of the inventions disclosed in the present application will be explained in brief as follows:

[0024] According to the present invention, it is not necessary to measure oscillation frequencies in all frequency bands in advance and store them in a memory. Therefore, the time taken until a used frequency band is decided, becomes short and the occupied area of a circuit can be reduced. Since there is provided a delay compensating circuit which applies a delay to a signal divided by a variable divider, it is possible to avoid that a frequency band improper due to a delay in reset signal or the like is selected.

[0025] Further, according to the present invention, it is possible to prevent solid variations from occurring in the accuracy for determination of a frequency band due to variations in manufacture and improve yields. Further, since a delay compensating circuit is used to detect a shift in timing of a signal and apply a delay to a signal divided by a variable divider in accordance with the result of detection, an accurate frequency band can be determined while increases in circuit area and chip size are being suppressed.

Problems solved by technology

This is because when an attempt is made to bring a capacitive element having a capacitance value necessary to obtain a desired characteristic into on-chip form, the area of the element becomes very large.

However, thermal noise of the resistive element increases with the increase in resistance value.

The PLL is accompanied by a problem that since the voltage of the loop filter is directly applied to a control terminal of the VCO, the thermal noise produced in the resistive element appears on the output of the VCO when the thermal noise of the resistive element constituting the loop filter is high and the control sensitivity of the VCO is high.

However, it has been fount out that a problem arises in that when such a system that the actual frequencies are measured over all the frequency bands in advance and stored in the memory to decide the oscillation frequency band to be used, is applied as in the invention of the previous application where the number of the oscillation frequency bands for the VCO increases, the time required to measure the frequency of the VCO becomes long and hence power consumption increases, and the capacity of the memory that stores the result of measurement must be increased, thus leading to an increase in chip size.

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